No cold water pressure after Water went off for a bit

hi, its quite possible that when shutting off the isolation valve and re-opening the valve got stuck or has snapped half open inside, when you isolated the water did it isolate both the bathroom and kitchen or just the bathroom? if the answer is the latter then that is more than likely your problem, I have also had this problem in the past where the bathroom had lost pressure since isolating the water via the cold water storage cistern in the loft and by doing so I had introduced some debris from the bottom of the tank into the pipework and this prevented the flow of water.

If is fed from a storage tank you might have a little airlock,if you stopped the water from a gate valve/SD valve that might be gone

If you have cold water storage in the loft and you empty it when you repaired the the cistern, I think it is a air lock in your system so you will have to force it through the kitchen tap, By covering the whole of the tap by Pressing-strong with your hand and open the cold water and then open hot water. To push back the airlock in the water tank .

Hi- your kitchen tap would be mains fed hence no pressure issues. I’m assuming you have a tank in the loft? If yes and it’s metal, then you may have a blockage or more likely an airlock. Go down the airlock route first. Difficult to explain what to do on this feed. Go onto YouTube and search airlock in tank fed water system. You’ll need a short length of hose/pipe. If you have a mains fed bathroom then likelihood its a faulty isolation valve. Hope this helps.